1. Field of the Invention
This invention relates to an apparatus and method for a shift control, and more particularly, to a shift control apparatus and a shift control method for an automotive automatic transmission equipped with a clutch device adapted to be engaged and disengaged in response to both a shift command and a clutch pedal manipulation.
2. Related Art
Automatic transmissions which realize automated gearshift operations have been widely used as automotive transmissions. Among them, torque converter-equipped automatic transmissions are chiefly used for small vehicles. In large vehicles such as buses and trucks which require a large driving torque, it is difficult for a torque converter to adequately transfer the large driving torque.
In this respect, an automatic transmission equipped with a gear transmission similar in construction to a conventional manual transmission and a clutch adapted to be automatically engaged and disengaged has been developed for use in large vehicles. In the automatic transmission of this kind, the engagement and disengagement of the clutch are automatically controlled in timed relation with a shift timing determined by a shift command, so that a smooth automatic speed change may be achieved.
Another type of an automatic transmission developed hithertofore is provided with a clutch whose engagement and disengagement are not only automatically controllable in response to a shift command but also executable in response to a clutch pedal manipulation by a driver.
The above-mentioned conventional automatic transmission which allows both automatic and manual clutch operations is so designed that the automatic clutch on-off control, i.e., clutch engagement/disengagement control, and the automatic shift control are prohibited so long as the clutch pedal is depressed, whereby a priority is given to a driver's intention such as a driver's clutch-slipping manipulation. With this arrangement, even if a shift command giving instructions for an automatic gear shifting is delivered, neither the clutch on-off control nor the automatic shift control is carried out while the clutch pedal is being depressed.
According to this arrangement which completely prohibits the automatic gear shifting during the depression of the clutch pedal, if an intense braking is applied while the clutch pedal is depressed deeply, an automatic gear shifting is kept prohibited even if a gear position presently established is no longer proper. This entails a problem that a smooth vehicle acceleration cannot be achieved when the driver attempts to accelerate a vehicle after releasing the clutch pedal because a mismatch takes place between the vehicle speed and the gear position established.